cubrid_set_db_parameter() can be used to set the database transaction isolation
level and lock timeout value.

- Change the default status of auto commit mode to off.

Fixed bugs:

- Fix a bug in cubrid_bind: When the value of binding parameter is NULL, it will covert the value to empty string;
- Fix a bug about BLOB/CLOB: When inserting LOB data, if the data size is large enough, it will fails. And if the LOB data is in a file, and it is too large to be put into memory, you can bind a file path name when binding the LOB data;
- Fix a bug about CLOB: When binding data type is CLOB, it will fail when inserting it into CUBRID;
- Fix a bug in cubrid_stmt_describe_col which will cause the failure of test bug_44861.phpt;
- Fix a bug in cubrid_handle_quoter: Before escaping unquoted string, it should init the value of quotedlen to 0.